Just need to add the opening and closing of the file handles

use strict;
use warnings;

my $infile = 'data.txt';
my $outfile = 'newdata.txt';

open my $in_fh, $infile or die $!;
open my $out_fh, '>', $outfile or die $!;

my %hash;
while (<$in_fh>) {
    chomp;
    my @data = split /\s+/;
    push @{$hash{$data[0]}}, @data[3,4];
}

for my $key (sort keys %hash) {
    print $out_fh join(' ', $key, @{$hash{$key}}), "\n";
}

close $in_fh;
close $out_fh;
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